JP4246378B2 - Device used in vivo compatible with magnetic resonance imaging procedures - Google Patents

Description

【００２７】
ここで、ＪΦ（ｍ、ｋ）は、上の式において下記の式で定義される表面電流密度の方位角成分を示す。
【００２８】
【数２】

【００２９】
また、Ｉｍ（ｔ）およびＫｍ（ｔ）は、２種のｍ位の変形ベッセル関数を示し、ｍは整数（たとえば、１、２、３、．．．．．）であり、Ｉ’ｍ（ｔ）およびＫ’ｍ（ｔ）はＩｍ（ｔ）およびＫｍ（ｔ）の一次導関数を表す。
コイルに関連する蓄積磁気エネルギーは下記の通り級数展開式の形で示される。
【００３０】
【数３】

【００３１】
特に表面電流密度がｚ成分を持たないソレノイド・コイルまたはｚコイルの場合、エネルギーおよび磁界に関する上記の式は、下記のとおりに単純化される。
【００３２】
【数４】

【００３３】
いくつかの空間位置で一組の磁界拘束条件を満たす円筒表面の電流密度分布に関する最適の（またはエネルギーが最小の）解決法を見つけるために、エネルギー汎関数構成が下記のとおりに定義される。
【００３４】
【数５】

【００３５】
ここで、１組のＬ乗数を表す。磁界拘束条件は、対象結像容積の数点において１組の望ましい磁界値を規定する。
電流密度汎関数に対するエネルギー汎関数を最小限にするために、電流密度汎関数に下記のとおり変分を加える。
【００３６】
【数６】

【００３７】
次に、最適化された電流密度がＬ乗数について下記のとおりに表される。
【００３８】
【数７】

【００３９】
ＪΦ（ｚ）は、望ましい磁界分布の場合ｚで非対称なので、そのフーリエ成分は下記のとおりに表すことができる。
【００４０】
【数８】

【００４１】
電流密度に関する式を磁界拘束条件式に挿入すると、乗数λに関する１組の１次方程式が得られる。
【００４２】
【数９】

【００４３】
ラグランジュの乗数について磁界拘束条件１次方程式を解くと、このラグランジュの乗数を含む式から電流密度を決定できる。限定長さ（Ｌ）のＲＦコイルの場合、表面電流密度は正弦級数式で望ましい位数まで展開できる。
【００４４】
【数１０】

【００４５】
ここで、ｋｎの値は下記のとおりである。
【００４６】
【数１１】

【００４７】
また、Ｊｎは、電流密度に関する膨張係数を示す。
次に、限定長さのコイルの表面電流密度についてｋ空間における一般式を下記のとおりに表すことができる。
【００４８】
【数１２】

【００４９】
ここで、Ψｎ（ｋ）は、下記の式で定義されるｋの奇関数である。
【００５０】
【数１３】

【００５１】
新しい関数展開式を使って、蓄積磁気エネルギーおよび磁界に関する式を下記のとおりに表すことができる。
【００５２】
【数１４】

【００５３】
コイル外部の望ましい受信フィールド分布は、いくつか選択された位置の数個の磁界拘束条件ポイントに変換することができる。各設計ごとに、磁界拘束条件ポイントが下記のとおりに定義される。
【００５４】
【数１５】

【００５５】
拘束条件は、相対的な磁界強度のほかにギャップにおいて要求されるコイルの磁界の均質性を規定する。様々な点での半径成分に関する磁界拘束条件式は下記のとおりに表すことができる。
【００５６】
【数１６】

【００５７】
便宜上、磁界の式およびエネルギー式は両方とも行列で表される。２つの式の間で、ｂの行列要素は下記のとおりに示される。
【００５８】
【数１７】

【００５９】
コイルの蓄積磁気エネルギーは、下記のとおりである。
【００６０】
【数１８】

【００６１】
ここで、エネルギー行列要素は下記の式で示される。
【００６２】
【数１９】

【００６３】
磁界拘束条件式を含むエネルギー汎関数は下記のとおりに定義される。
【００６４】
【数２０】

【００６５】
エネルギー汎関数の最小条件を求めるために、電流列ベクトルＪに対してＦ汎関数を最小にする。すなわち、
【００６６】
【数２１】

【００６７】
こうして、電流密度を含めた下記の最小条件方程式にたどり着く。
【００６８】
【数２２】

【００６９】
別の独立方程式として下記の磁界拘束条件式を使用する。
【００７０】
【数２３】

【００７１】
まず、ラグランジュの乗数を、上の最小条件式および磁界拘束条件式を組み合わせた下記の１次方程式において解くことができる。
【００７２】
【数２４】

【００７３】
ラグランジュの乗数にこの値を使って、コイルの表面電流密度を下記のとおりに決定することができる。
【００７４】
【数２５】

【００７５】
また、電流密度は下記のとおりである。
【００７６】
【数２６】

【００７７】
コイルの半分の総電流は下記の式で示される。
【００７８】
【数２７】

【００７９】
巻きの数がＮｔｕｒｎに設定される場合、個々の電流は下記のとおりに決定できる。
【００８０】
【数２８】

【００８１】
コイルの半分でＮ巻きのコイルのインダクタンスは下記のとおりである。
【００８２】
【数２９】

【００８３】
各電流腹部のポジションを決定するために、コイルの中心から下記の電流密度の積分を計算する。
【００８４】
【数３０】

【００８５】
この積分により、Ｎ個の異なる離散的電流ワイヤ・ループ全体のすべての空間的間隔を求めることができる。ｚ軸に沿った各ワイヤの正確な位置は、該当の間隔の質量の中心として決定することができる。
【００８６】
【数３１】

【００８７】
要するに、相対する対のマイクロコイルの各マイクロコイル内におけるコイルのコイル内分布を最適化するための手段は、電流の効果、コイルの特性および個々のコイルまたは巻き線のポジショニングおよび設計に関する以上のようなまたはこれに代わる数学的モデルを土台とすることができる。この特殊な構図は、円筒形のＲＦコイルのために開発されたものであり、この技術は、脈管内、窩腔内、実質内または管内ＭＲ映像コイルの電流腹部位置の設計を最適化するための簡単な手順となる。
【００８８】
図４（ａ、ｂおよびｃ）を参照すると、コイル内設計の修正が本発明のカテーテルの性能を向上させる様子を理解するのに役立つ。図４ａは、ギャップの中点（例えば、図１のスペース１９によって表される２ｄの距離で分離された相対するマイクロコイルの最近端間の真中）からの距離の関数として磁界強度（ｙ軸）を示している。図４ａは、個々の巻き線のサイズおよび巻き線間の間隔が同じである相対する対のマイクロコイルを持つ円筒形装置における磁界強度の関係を示している。図４ａから分かるとおり、最大磁界強度Ｆｍａｘは比較的急なピークを描き、ギャップの中心（ｘ＝０）からの距離が変化するにつれて、磁界強度は減少する。ギャップの真中（相対するマイクロコイルの相互に一番近い端からｄの距離）と相対するマイクロコイルの端の間の中ほどで、磁界強度は大幅に、通常Ｆｍａｘの２５％から５０％低下する。この急速で大幅な磁界強度の変化は、ある種の処置において画像のタイプおよび品質を提供する装置の機能を減ずる可能性がある。図４ｂは、上に論じたモデリングに関する考慮事項に従ったマイクロコイルの位置、形状、厚みおよび分布の設計により得られる磁界強度分布の理想的な形を示している。個々の巻き線の効果は上に示されるとおり数学的に計算できるので、個々の効果を加算して、有効磁界強度を決定できる。個々の巻き線の効果の数学的加算にはある程度の相互作用的効果を考慮して、コイルの組み合わせから得られるより現実的な磁界効果に合わせることができる。さらに到達可能な磁界強度分布が図４ｃに示されている。この図には、理想的という点では劣るが、大幅に改良された磁界強度分布が示されている。図４ｃは、磁界強度と円筒形装置に沿った位置の関係を示しており、装置は、相対するコイルの近端の間に２ｄの間隔を置いて相対する対のマイクロコイルを持ち、対のマイクロコイルは異なる間隔（例えば、巻き線１３と１５の間の間隔が同一のマイクロコイルの巻き線１５と１７の間の間隔に比べて異なる）のコイル巻き線部分（図１においては、例えば１３、１５および１７）を持つ。磁界強度は、図４ａに示される相対するマイクロコイル構造の場合に比べて、ギャップ中心（ｘ＝０）付近でより均等になる。磁界強度は、ギャップ中心からの距離が大きくなるにつれて減少するが、減少速度は、図４ｂの理想的結果に比べれば大きいが、図４ａの均等コイル巻き線の場合より小さい。ギャップ中心とギャップ中心からマイクロコイルの近端までの距離の半分であるｄ／２位置の間での磁界強度の低下は２０％以下と予想される。Ｆｍａｘとギャップ中点とマイクロコイルの近端の間の真中であるｄ／２ポイントでの磁界強度の間の減少は１７％未満が望ましく、１５％未満であればもっと望ましく、さらには１２％未満が望ましく、一番望ましいのは１０％か８％未満である。
【００８９】
本発明に基づく装置は、対のマイクロコイルの各マイクロコイル間に間隔を置いて相対するＲＦレシーバ・マイクロコイルを少なくとも１対持つエレメントから成り、前記ＲＦレシーバ・マイクロコイルが各々少なくとも３つの個々のコイルを持ち、前記の少なくとも３つの個々のコイルが前記のマイクロコイル内の少なくとも２対の個々のコイル間の間隔が少なくとも１０％異なるように隣接するコイル間に間隔を持つ、生体に使用するための医療装置として説明することもできる。ギャップ内の磁界強度分布の結果を改良するために、対の個々のコイル（または巻き線）間の間隔は、マイクロコイルが属し円筒（またはその他の形状）の軸に平行の平面内にある線に沿って測定して、隣接する巻き線間の他の間隔に比べて少なくとも１２％、１５％あるいは２０％かそれ以上の違いにすることができる。
【００９０】
本発明の実施において有益な構造に使用できる別の設計構成は、１対のマイクロコイルの半分を形成する領域に２層のマイクロコイルを持つ構成である。つまり、ギャップの方向に傾く第１のマイクロコイルのセットをＭＲ観察可能装置の１つの層に配置し、第２のマイクロコイルのセット（たとえば、１組の巻き線）もギャップの方向に傾かせるが、第１のマイクロコイルのセットの上または下に重なる絶縁層内に配置することができる。同様の傾きのマイクロコイルのセット内におけるコイル間の間隔は、同じ幅でも異なる幅でもよく、同じまたは異なるコイル間の間隔で、同じ角度でも異なる角度でもよい（両方ともギャップ方向に傾くか、両方ともギャップと反対の方向に傾かなければならないが）。この装置は、少なくとも１組のマイクロコイルを持つことができ、前記の少なくとも１対のマイクロコイルの半分が隣接する巻き線間で少なくとも３つのスペース、スペース１、スペース２およびスペース３を持つ少なくとも４つの巻き線から成り、前記の少なくとも３つのスペースのうち少なくとも１つが前記スペースのうち少なくとも他の１つと異なる寸法を持つ。
【００９１】
技術上周知の技術および構造上の考慮事項の一部は本発明の新規の構造設計に使われているが、技術上周知の多くの技術および構造上の考慮事項を本発明の実施に含めることができる。たとえば、ルーメン４、支持材料３４およびカテーテル・ケーシング４０の組成を、医療用に開発された既知の生体適合性の材料から選ぶことができる。カテーテル・システムの一部を構成するマイクロコイルおよび回路は、これまで医療装置の分野で使用されたことがない技術でもこれを使って、提供することができる。たとえば、マイクロコイルは、導電体（特に銅、銅被覆材および技術上周知のその他のＲＦアンテナ材）のフィラメントをラップすることにより、またはルーメンの上にフィラメントを形成することにより提供することができるだろう。このような形成プロセスには、沈積プロセス、成長沈積プロセス、沈積エッチング・プロセス、マイクロリトグラフィ、マスキング沈積などが含まれる。沈積プロセスには、めっき、無電解めっき、スパッタリング、有核成長（たとえば第４，７７５，５５６号および４，７１０，４０３号）、高エネルギー沈積またはエッチング・プロセス（たとえば、米国特許第５，３８９，１９５号および５，３３２，６２５号）、化学的沈積およびエッチング・プロセスなどを含めることができる。米国特許第５，１０６，４５５号、５，１６７，６２５号および５，２６９，８８２号において示される回路および配線を作るための技法は、フィラメント製品および表面に回路を沈積するために一般的に有益なその他の技術の例である。
【００９２】
図２は、本発明において使用できる１つの構成に基づくカテーテル１００の中間部分の断面図である。マイクロカテーテル１０２は、マイクロカテーテル１０２の一端１０５がカテーテル１００の壁の穴１０８からカテーテル１００の外に伸びるように、内部案内エレメントまたはデフレクタ１０６に接して反っているところが示されている。マイクロカテーテル１０２は、デフレクタ１０４によって反って、接点１０３からデフレクタ１０４に支えられる。穴１０８は、図２においてカテーテル１００の実質的壁を構成する材料の３つの層１１０、１１２および１１４として示されるものを貫通する。デフレクタ１０４は、マイクロカテーテルを穴１０８に導き入れこれに通すための案内となる。カテーテルの外に出るマイクロカテーテルごとに穴およびデフレクタが１つあり（これらのマイクロカテーテルは自身の固有のマイクロコイルを持つことができる）、これらのマイクロカテーテル（図には示されていない）はカテーテル１００から外に伸びる。ただし、２本以上のマイクロカテーテルが単一の穴から出る場合はこの限りではないが、これは、マイクロカテーテルの効果（たとえば、薬物送達）の大部分がカテーテル１００の表面に対して小さいエリアで生じることになるという理由で、望ましい構造ではない。この装置は、少なくとも３つの別個のポートから少なくとも３本のマイクロカテーテルの各々の方向を定めるために少なくとも３つのデフレクタを持つことができる。
【００９３】
図２には、１対のマイクロコイル１１６および１１８も示されている。これらのマイクロコイル１１６および１１８は、カテーテル１００の層１１２の中に埋め込まれているところが示されている。カテーテル１００の映像化および位置設定機能が最適に働くために、マイクロコイル１１６および１１８によって発せられる信号が可能な限り正確で明確であることが非常に望ましい。カテーテル内に他の回路およびワイヤが存在すると、この種の性能を妨害する可能性があるので、カテーテルおよびそのサブコンポーネントの各種部品の電気および電子機能妨害の問題を防止するために特に考慮しなければならない。例えば、それぞれマイクロコイル１１６および１１８の端１２４および１２６に接続されるワイヤ１２０および１２２は、電気的に接続するための点（例えば、端１２４および１２６）以外ではマイクロコイル１１６および１１８に接触してはならない。これは、本発明の実施に基づき様々な方法で可能にすることができる。この種の問題が生じる可能性は近位のマイクロコイル１１６においては構造的に小さい。なぜなら、その端１２４をコイル回路を通らずにワイヤ１２２に接続できるからである。従って、ワイヤ１２２をコイル１１６と同じ層１１２に配置することができる。遠位のマイクロコイル１１８の場合、ワイヤ１２０を２つのコイル１１６および１１８越しに通さなければならず、マイクロコイル１１６および１１８に接触したり、容易にマイクロコイルからの信号に干渉する可能性がある。これを防止するために、マイクロコイル１１６および１１８は、単一の層１１２内に示されているが、遠位マイクロコイル１１８からのワイヤ１２０は、コイル１１６および１１８またはカテーテル１００内のその他の回路（図には示されていない）への電気的または電子的な干渉またはこれとの相互作用を減少または排除するために、層１１４内に示されている。素子の適切な位置設定の必要性が認識されれば、一般的な製造技術において利用できる多数の技術を使って、それぞれの素子を別個の層に分離することができる。たとえば、マイクロコイルを設置した後（例えば、ラップ、沈積またはエッチングにより）、ポリマーまたはその他の絶縁材により１つの層（例えば、層１１２）にマイクロコイルを閉じ込めることができる。この保護層または囲い込み層が確立されたら（適切な電気接続点を他の電気または電子接続のために維持して）、他の配線または回路をこの被覆囲い込み層（たとえば、層１１２）の上に構築することができる。この追加の配線または回路はコイルを作るために使われるプロセスと同様のプロセス、またはラップ、予め作られた回路の応用、回路またはワイヤ素子の沈積、回路またはワイヤ素子のエッチングおよび技術上周知のその他の構造またはミクロ構造技術など技術上周知のその他のプロセスにより構成できる。本発明の一部の構成の実施にこの選択的構造を使用する主な目的は、カテーテルの異なる層（同じポリマー結合材組成であっても）内に回路および（または）配線を配置することである。配線または追加の回路の配置は、クロストーク、干渉、相互作用またはその他マイクロコイルおよび回路の性能を損なうような関連効果を最小限に抑えることを意図して行われる。上記の考慮の際に、それぞれの素子の配置設計において、固有の干渉波効果または磁界効果を考慮することができる。
【００９４】
本発明の一部の態様に基づくＭＲ画像監視薬物送達用複合カテーテルは、治療中のＭＲ映像（分光分析）監視またはその他の生理学的監視のためにマイクロイメージング・コイルが組み込まれた複合装置（針またはカテーテル）またはその他の装置に関わる。コイルのすぐ近くの領域ならびに治療場所の病理学的変化を非常に高い信号雑音比で投与プロセスを妨害することなく画像化するために、マイクロ・コイルを、従来のＭＲスキャナにインターフェイスすることができる。この種の装置は、多くの神経学的実質間（ｔｒａｎｓｐａｒｅｎｃｈｙｍａｌ）または脈管内治療用として近い将来非常に需要が大きくなるだろう。
【００９５】
複合装置の１つが図１に略図的に示されている。図１に示されるとおり、カテーテルは、生理学的測定、薬物送達、材料の引き上げ、サンプリング、温度緩和または変動、電気刺激など様々な機能を果たすためにルーメン４の中に多数のマイクロサイズのチューブ２４、２６、２８および３０を持っている。カテーテルの先端には、ＭＲ映像および分光のための微小な前置増幅装置２２といっしょにマイクロコイル１０がある。
【００９６】
一般的に言って、この種の複合装置（つまりカテーテル）は、図２に示されるとおり下記の４つのモジュラー部分に分解できるマイクロイメージング・コイルを少なくとも１つ含む。
１）最適化されたイメージング・コイルまたは電極
２）前置増幅および減結合集積回路
３）信号送信および遮蔽
４）遠隔整合回路
上記の４つの部分は、個々の複合装置設計の場合必ずしも相互に分離されないが、以下の説明を容易にするためにのみモジュールを分離する。
【００９７】
ほとんどの場合、これらのモジュールの一部は１つの複合装置に統合されることが多い。ＭＲ映像のためのマイクロコイルは、シングル・ループ、より線、２つの相対するソレノイドのうち１つとすることができる。これらのコイル設計はすべて、コイルの近接領域に対して非常に敏感である。個々のコイルの空間的感度動向の詳細は、その導体のパターンに依存する。
【００９８】
相対するソレノイドの場合、受信のための一次磁界フラックスは２つのコイルの間のギャップではじき出される（一般的に巻き線にあるいはコイルが巻かれるまたは形成される円筒形装置の軸に直交する方向に）。必要な巻き線の数はコイル当たり少なくとも３であり、３から２０の間が望ましく、４から１６までがさらに望ましく、もっとも望ましいのは５から１２までの巻き線であり、各コイルの直径は可能であれば０．１から２．４ｍｍとし、直径０．３から２．０ｍｍを使用すればもっと望ましく、０．５から２．０ｍｍの直径を使用すれば最も望ましい。コイルを表面に沈積することにより、カテーテルのサイズに応じてコイルとして材料の薄い層を沈積して（例えば、数ミクロンの厚みからコイルの幅と同じ厚みまで可能である）、コイルによって占める体積を小さくし、コイルの幅を広くすることができる。コイルは小さい直径の円筒形表面に巻かれるか沈積されるが、最適化のための自由度がいくつかある。ソレノイド・コイル設計の場合、自由度の１つは、巻き線間の間隔である。マイクロサイズのコイルの設計は、ある程度まで、特定の臨床用装置によって課せられる形状的制約の下で空間的に望ましい受信フィールド・パターン（均等性）を生じるために、数値的に最適化することができる。ターゲット・フィールド法を使って、導体パターンを、ターゲット受信フィールド・パターンにほぼ整合するように数値的に最適化することができる。マイクロコイル内のコイルは、隣接するコイルの中心間の間隔をコイル直径の２．０倍（隣接するコイルの外面間の間隔が個々のコイルの直径に等しくなるように）から１０倍（隣接するコイルの外面間の間隔が個々のコイルの直径の９倍になるように）として形成するか巻くことができる。間隔は直径の２．５から８倍の間が望ましく、もっと望ましいのは３倍から６倍の間である。前に述べたように、先行技術は、２．８ｍｍ未満の直径のマイクロコイルの使用は望ましくないことを示唆している。コイルが相対していて傾いていれば、本発明の実施においてコイル直径を２．４ｍｍ以下とすることが望ましい。本発明においては、対のコイルの各半分で異なるコイル内間隔を持つマイクロコイルを提供すること、および望ましい２．４ｍｍ未満より大きいコイル直径を持つことも新規である。例えば、コイルは、コイル内間隔を本発明の教訓に従って変動する場合、もっと小さい望ましい寸法を含めて、簡単に４．０ｍｍに、３．５ｍｍあるいは３．０ｍｍにすることができる。
【００９９】
さらに、コイルのワイヤの材料は、非磁気性金属または人間の組織と同様の磁化率を持つ金属合金とすることができる。例えば、望ましい材料としては、銅、銀、アルミニウムおよび銅・アルミニウム合成物がある。銅も銀も反磁性であり、アルミニウムは常磁性である。磁界かく乱を最小限に抑えるために、コイル導線を異なる金属材料の複数の同心層を持つように作ることができる（Ｃｕχ＝−９．７×１０^−６およびＡｌχ＝＋２０．７×１０^−６）。異なる金属成分の正確な層の厚みまたは半径は、ワイヤのサイズに応じて数値的に最適化できる。ゼロ磁化率の円筒形ワイヤの場合、半径比は下記の式で与えられる。
【０１００】
【数３２】

【０１０１】
マイクロコイルと画像励起に使われるボリューム・コイルの間の相互結合を最小限に抑えるために、減結合回路をマイクロコイルに組み込むことが望ましい。励起中、減結合回路素子は、イメージング・コイルの共鳴周波数を送信ＲＦ周波数から外すことによって、マイクロコイルをボリューム・コイルにとって見えないものにする。コイル減結合要件を満たす設計の１つが図３に示されている。装置が、Ｄで示されるＰＩＮダイオードを２つのコンデンサ（Ｃ１およびＣ２）と直列に含む場合、イメージング・コイルはＬとして抽象的に示されている。ＰＩＮダイオードＤは、ダイオードを横切る外部制御電圧Ｖｄによって能動的にオン・オフが切り替えられる。ダイオードＤがオンに切り替えられると、コイルＬおよび２つのコンデンサＣ１、Ｃ２は、周波数に同調された共鳴回路を構成する。これは、前置増幅装置を含む回路の改良版である。装置は、１台だけのコンデンサと直列のＰＩＮダイオードを含むこともできる。ダイオードは外部制御電圧によって能動的にオン・オフが切り替えられる。ＲＦ周波数の信号増幅のためにＦＥＴ（電界効果トランジスタ）を備えることができる。ＦＥＴ素子またはその他のタイプの前置増幅モジュールをＲＦ励起中保護するために、ＦＥＴの前にクロス・ダイオードを配置して、ＲＦ送信中過剰に誘導された電流をバイパスすることができる。
【０１０２】
コイル全体を複合にすることができる。言い換えると、カテーテルに沿った複数の場所で同時に映像化するために、イメージング・コイル全体を直列にまたは位相配列に接続された複数のコイル素子で作ることができる。上記の複数のコイルすべてが幾何学的に同じ形状でも、異なる形状でもよい。イメージング・コイルは、非局部的にすることもできる。つまり、コイルをカテーテルのかなりの長さに沿って空間的に分散することができる（特に、上に示したモデリングを考慮することにより）。このために、能動コイル素子には、より線、２本の平行なワイヤ、同軸ケーブル、これらの組み合わせなど、多くの選択肢がある。
【０１０３】
イメージング・コイル素子の選択肢の多様性のほかに、マイクロ電極などその他の様々な素子を、細胞または膜の電位測定、圧力／流量監視またはその他の生理学的監視のための装置に組み込むことができる。
信号雑音比（Ｓ／Ｎ）を最適にするためまたは雑音値を最小限に抑えるために、検波されるＭＲ信号は、できる限りコイル素子に近い場所で即時増幅されること（たとえば前置増幅）が望ましい。実際のカテーテル形状は、従来の増幅素子を使用するための十分なゆとりはない。前置増幅など様々な信号の予備調整に使われる電子素子のサイズを最小限に抑えるために、イメージング・モジュール付近に集積回路モジュールが取り入れられている。集積回路モジュールは、前置増幅装置（またはＲＦ周波数の装置）およびシリコン・チップに組み立てられるその他の補助装置を含む。シリコン・チップは４ｍｍ２未満のサイズであることが望ましい。集積回路モジュールは、特定の機器設計と形状的に両立する小型の非磁気ケーシングの中に収められることが望ましい。もっとも単純な装置の１つとして、単一のＦＥＴ素子しか含まないものが考えられる。もっと複雑な回路を組み立てて性能をよくするために、集積回路技術の助けを借りて、１つのシリコン・モジュールにもっとも多くの素子を組み込むことができる。
【０１０４】
望ましい送信モジュールは、その後の信号の増幅およびその他の処理のためにコイルから遠隔ターミナルにＭＲ映像化のために検出されるＲＦ信号を送信するための、カテーテルに沿ったたわみケーブルの一部である。望ましい設計においては、ケーブルのすべての素子がカテーテルに組み込まれる。ケーブルの望ましい要件の１つは、微細なＭＲ信号に対する信号減衰を小さくすると同時に雑音汚染をわずかにすることである。ケーブルに関するその他の要件は、カテーテルのフレキシビリティおよび硬さへの妨害を最小限にすることである。この要件を満たすために、装置には下記の通り多くの多様な代替形態がある。
【０１０５】
１）３層同軸ケーブル（中心の導線が同心の２層の遮蔽材で囲まれるケーブル）。このケーブルのバリエーションは、中心の導線がケーブルの中心軸に沿ってらせん状に巻かれるものである。
２）遮蔽より線ケーブル（中央の２本のより線が同心の遮蔽材の層で囲まれるケーブル）。このケーブルの１つのバリエーションは、２本のワイヤがケーブルの中心軸に沿って渦巻き状またはらせん状に巻かれるものである）。
【０１０６】
３）遮蔽平行双極ケーブル（２本の平行の双極ワイヤが中心軸に対して対称的に配置され、同心の遮蔽材の層で囲まれるケーブル）。このケーブルの１つのバリエーションは、２本のワイヤがケーブルの中心軸に沿って平行に渦巻き状にまたはらせん状に巻かれるものである）。
遮蔽層としては、細い編組導線の層、金属フィルムの層あるいは本発明の実施に適合する寸法で供給できる技術上周知のその他の遮蔽材（望む場合には、接地できる）の層が可能である。
【０１０７】
さらに別の有益な設計は、すべての素子を遠隔装置（または遠位端）に置くという考え方である。図３に略図的に示される回路図は、イメージング・コイル（マイクロおよびマクロ）、送信線、移相ネットワーク、同調および減結合回路およびバラン（平衡不平衡インピーダンス整合変成器）を含んでいる。Ｚは、減結合回路の一部としての同調素子（ＬまたはＣ）を表す。送信線と移相ネットワークの組み合わせは、１／４または半波長特性を示す。
【０１０８】
遠隔整合装置とは、装置の遠隔端に配置される装置である。この遠隔装置は、先端のイメージング・コイル用の特別な同調装置としても、離調（または減結合）装置としても使用できる。遠隔整合装置は、コイル・インピーダンス整合および周波数同調のために送信装置の効果的なインピーダンス変成を考慮に入れている。この設計においては、送信線および遠隔装置の両方が、同調および離調のために使われる。送信線の特性を利用するために、無線周波数の１／４または半波長のワイヤが使用される。そうでなければ、同じ有効な１／４または半波長行動を示す移相ネットワークを持つ送信線を使用することができる。コイル同調はコンデンサまたはインダクタを使って行える。さらに、装置のサイズは幾何学的には制限されない。このモジュールの装置サイズは問題にはならないので、従来の電子素子をもっと使用できる。個々の設計に応じて、遠隔装置は非常に重要にもなりうるし、重要でない場合もある。
【０１０９】
最後に、カテーテル先端には安定化メカニズムが組み入れられる。望ましい安定化装置は、機械的に駆動できるか、形状記憶合金で作られ外部電圧信号により制御される。
【図面の簡単な説明】
【図１】 図１は、本発明の実施に基づく薬物送達用カテーテルを示す。
【図２】 図２は、カテーテルのマイクロカテーテル出口およびカテーテルの配線を強調したカテーテルの断面図である。
【図３ａ】 図３ａは、本発明のカテーテルの回路略図である。
【図３ｂ】 図３ｂは、本発明のカテーテルの回路略図である。
【図４ａ】 図４ａは、３つのマイクロコイル構造に関する磁界強度対相対する２対のマイクロコイル間のギャップ中心からの距離のグラフを示している。
【図４ｂ】 図４ｂは、３つのマイクロコイル構造に関する磁界強度対相対する２対のマイクロコイル間のギャップ中心からの距離のグラフを示している。
【図４ｃ】 図４ｃは、３つのマイクロコイル構造に関する磁界強度対相対する２対のマイクロコイル間のギャップ中心からの距離のグラフを示している。[0001]
[Technical field to which the invention belongs]
(Field of Invention)
The present invention relates to medical devices compatible with procedures performed during magnetic resonance imaging (MRI), particularly during procedures observed using magnetic resonance (MI) imaging techniques. Drug delivery It relates to a medical device that can be used.
[0002]
[Prior art and problems to be solved by the invention]
(Technical background)
Medical procedures can now be performed on a relatively small area of the patient. Minimize into small cell clumps, in veins and arteries, or at remote parts of the body without surgical incision of the body Invasion Treatment can be performed using conventional techniques. Balloon angioplasty, microsurgery, electrotherapy and Drug delivery Such as minimizing the procedure without performing a large incision on the patient. Invasion However, it is necessary to develop a technique so that the treatment can be seen simultaneously with these treatments. X-ray imaging, such as fluoroscopy, is a possible method for observing the treatment site, but long-term X-ray irradiation is itself harmful to the patient. Optical fiber observation of the treatment site does not cause harmful radiation to the patient, but the optical fiber occupies too much space to provide the light needed for observation and the path to return the light, and cannot be more than the surface image ( In other words, only the surface of the internal object can be observed from the position where the optical fiber device is disposed). Optical fiber or direct light observation is within the real Drug delivery Or intravascular Drug delivery Or, it is more suitable for medical treatment such as gastrointestinal tract than microscopic treatment such as treatment.
[0003]
By using an MR receiver coil in the device tracked by the MR imaging system, Conform Techniques for observing a relatively large part of the device have been developed so far. Design considerations, especially for devices that have MR observation capabilities and specific treatment functions, especially for devices where the relationship between a specific treatment and MR receiver coil must be optimized for both treatment process and MR observation capability There is not much.
[0004]
US Pat. No. 5,211,165 Invasive A tracking system for tracking the position and orientation of a medical device, particularly a medical device that uses a radio frequency magnetic field gradient, such as a catheter, is described. The detection of the radio frequency signal is performed by a coil having a sensitivity trend that changes almost linearly depending on the position. this Invasive A typical device has a transmit coil attached near its end and is driven by a low power RF power source to produce a dipole field that can be detected by a receive coil array distributed around the subject's target site.
[0005]
U.S. Pat. No. 5,271,400 contains Invasive A tracking system for monitoring the position and orientation of a typical device is described. The device has an MR active sample and a receiver coil that is sensitive to magnetic resonance signals emitted by the MR active sample. Since this signal is detected when there is a magnetic field gradient, it has a frequency that is approximately proportional to the position of the coil along the direction of the applied gradient. The signals are detected in response to sequentially applied magnetic gradients that determine the position of the device in several dimensions. As shown in FIGS. 2a and 2b Invasive Each of the functional devices has an RF coil and an MR active sample incorporated into the medical device, and an MR active sample incorporated into the medical device.
[0006]
US Pat. No. 5,375,596 describes a method and apparatus for determining the position of devices such as catheters, tubes, placement guidewires and ports implantable in living tissue. The device can include a transmitter / detector unit having an AC radio frequency transmitter with an antenna and a radio signal transmitter disposed along the entire length of the device. The antenna is connected by a detachable clip to a broadband radio frequency (RF) detector circuit located in the transmitter / detector unit.
[0007]
U.S. Pat. No. 4,572,198 describes a catheter for use with an NMR imaging system that includes a coil winding to excite a weak magnetic field at the tip of the catheter. A loop connecting the two conductors supports a dipole field that locally distorts the NMR image and provides an image cursor on the magnetic resonance imaging display.
[0008]
U.S. Pat. No. 4,767,973 describes a system and method for sensing and moving objects in multiple degrees of freedom. The sensor system consists of at least one field effect transistor having a geometry selected to have the desired sensitivity.
Published PCT applications Nos. WO 93/15872, WO 93/15874, WO 93/15785 and WO 94/27697 show kink resistant tubing in which the catheter can include reinforcing coils and methods of forming tubing including the catheter. Yes. A layer of reinforcement can be deposited on the reinforcement coil.
[0009]
US Pat. Nos. 5,451,774 and 5,270,485 describe three-dimensional circuit structures that include a plurality of elongated substrates arranged in parallel and in contact with each other. Electrical elements are configured on the surface of the substrate along with conductors coupled to these elements. The conductors are selectively placed on each substrate so that they are in contact with conductors on adjacent substrates. The conductor pattern on the substrate may be spiral, circumferential or longitudinal. Radio frequency signals between the boards are transmitted and received using radio frequency signal transmission and reception circuitry and transmission and reception antennas on the boards (eg, column 7, lines 32-43). The circulation of coolant in the device is shown.
[0010]
U.S. Pat. No. 5,273,622 describes a continuous process for use with microstructures (including electronic microcircuits) on substrates and thin film semiconductor assembly systems, particularly elongated substrates such as fibers or filaments. ing.
U.S. Pat. Nos. 5,106,455 and 5,269,882 describe a method and apparatus for the assembly of thin film semiconductor devices using non-planar illumination beam lithography. A circuit formed in a cylindrical object is shown. US Pat. No. 5,167,625 Drug delivery Implantable multivesicles that can contain electrical circuits that react to signals that can be used (including wireless signals) Drug delivery Explains the system.
[0011]
PCT Application No. WO / 96/33761 (filed 15 April 1996) describes a parenchymal infusion catheter for administering a drug or other drug consisting of a pump coupled to the catheter. A porous tip is disposed at the distal end of the catheter, and the tip is porous to expel the drug or drug at the selected location. The catheter can be adapted for use during use by the telescoping portion of the catheter system.
[0012]
In "MR images of blood vessels by intravascular coils" (J. Mag. Res. Imag., February 1992, No. 4, p. 421-429), Martin, A. et al. J, Plewes, D.M. B. And Henkelman, R .; M.M. Describes a method for creating a high-resolution magnetic resonance (MR) image of a blood vessel using two coaxial solenoids separated by a gap region and a theoretical receiver coil design based on current flowing in opposite directions Yes. The coil diameter ranges from 3 to 9 mm. FIG. 3b appears to show that the sensitivity decreases as the coil diameter transitions from 9 mm to 7 mm, 5 mm, and 3 mm. The results of a study of the Q values of the opposed loop and the opposed solenoid coil show that the opposed loop coil showed a low W value and that the Q value is generally smaller when the Q diameter is small in the opposed solenoid design It shows that there was a trend. Within the scope of the study, it is stated that there is a compromise between the use of thicker wires to improve performance and the use of thinner wires to reduce overall coil dimensions. Decoupling circuits have also been shown to be useful in performing imaging functions using this catheter-based system in MR imaging. “Intravascular (catheter) NMR receiver probe: provisional design analysis and application to iliac femoral imaging of dogs” ( Magnetic Resonance In Medicine 24, 343-357-1992), Hurst, G .; C. Hua. J. et al. Duerk, J .; I. And Choen, A .; M.M. Explores the feasibility of a catheter-based receiver probe for NMR examination of arterial walls. Various design possibilities are being considered, including opposing solenoids (eg, FIGS. 2b and 3a and b). The catheter probe shown in FIG. 3 has a 100 pf capacitor and a probe that resonates at 64 MHz, with a 7.5 mm spacing between solenoids, a nominal solenoid diameter of 2.8 mm, and 5 turns of 28 gauge wire per solenoid. Configured.
[0013]
U.S. Pat. No. 5,429,132 describes a probe system that can be used during a medical procedure consisting of an RF sensing coil and a planar grid array of antennas spaced along the probe. Using the signal from the probe, the three-dimensional position of the probe is determined.
U.S. Pat. No. 5,445,151 describes a method for measuring blood flow acceleration and velocity using an MR catheter with a coil responsive to an RF signal. Multiple coils (eg, three coils) are placed in the invasive device, and a regular pattern of RF transmit pulses is emitted to produce a steady RF response signal. A second RF signal is transmitted from an RF coil disposed intermittently upstream. From the time delay and the distance between the RF coils, the velocity of the fluid is determined directly.
[0014]
U.S. Pat. No. 5,727,533 describes a catheter with an integrated electromagnetic identification device that can be used to determine the position of the catheter without the concomitant use of x-ray equipment. The electromagnetic field detection device includes a pair of leads incorporated into the catheter wall and a fine wire coil disposed at the distal end of the catheter. A core of magnetically permeable material can be placed inside the coil, such as a radiopaque strip.
[0015]
[Means for solving the problems]
(Summary of the Invention)
An element having at least one pair of opposed RF receiver microcoils with a space between each microcoil of a pair of microcoils, the coil diameter of the microcoil being of a useful size, eg 3 mm, 4 mm or more While possible, devices for in vivo use have been described that are less than 2.4 mm or less than 2.6 mm in many desirable systems. The device can be constituted by a catheter with at least one lumen, in which case at least one pair of microcoils are arranged radially around at least one lumen, the diameter of the coils being greater than 0.1 mm 2 Less than 4 mm (although a larger diameter wire can be used for the coil). The device may not have a port in the device, or at least one Drug delivery You can also have a port. At least one Drug delivery The port can be arranged such that at least some of the drug dispensed from the port is dispensed from a pre-device in the space between the microcoils. Drug delivery The port dispenses at least some liquid material in a volume formed by a surface extending radially from the catheter at the end of at least one pair of microcoils that form a space between each microcoil of the at least one pair of microcoils. To this end, a microcatheter that is within the device and extends out of the device can be included. The device is responsive to radio frequency transmission to produce a magnetic field having an average strength in a volume of comparable size surrounding the catheter located immediately above each of the microcoils, and more within the volume. Is generated. It is desirable that at least one pair of microcoils be embedded in a binding material surrounding the lumen. At least one pair of microcoils is electrically connected to the preamplifier within the portion of the device that is inserted into the body. When electrical connections are in the device, it is desirable that at least a portion of the electrical connections be formed in situ within the device.
[0016]
[Embodiment of the Invention]
(Detailed description of the invention)
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration preferred embodiments of the invention. The preferred embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, but other embodiments can be utilized and structural and logical without departing from the spirit and scope of the invention. It shall be construed that physical, architectural and electrical changes can be made. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof.
[0017]
Implementation of certain aspects of the present invention is applicable to all medical devices used in magnetic resonance imaging observation procedures performed concurrently with primary medical procedures. The features of the present invention that can individually have this general applicability in the field of medical devices include its MR Conform Included are types of RF response coils that are attached to the medical device to assure safety, circuitry coupled to the medical device, and means for orienting the microelement / microcatheter element, etc. within the catheter device. The preferred structure uses opposing solenoid orientations of the microcoil, the microcoil design is based on two coaxial solenoids separated by a gap region, and current is passed across the two coils in opposite directions.
[0018]
One aspect of the present invention uses opposing paired microcoils to accurately form a magnetic field around a device having a paired coil. Opposing pairs of coils differ in the angle of a coil or winding about one axis or between two sets of coils (eg, receiver coils) (with a positive angle rotation from the normal to the surface or Normally, this angle is either positive or negative with rotation at a negative angle). This angle is either out of the plane perpendicular to the axis of the object on which the coil is wound, or measured from that plane and positive for one coil. With respect to the other coil, it means a coil formed at a negative angle. Other developments in the potential field of implementation of the invention include circuitry connected to the coil, its shielding within the device, and decoupling circuitry coupled to the coil by wires. Meeting the wide range of functional needs of equipment Invasive The actual design and engineering details of a typical radio frequency detection medical device have so far been less specific. The present invention provides an essential advance to this type of device.
[0019]
Another important aspect of the present invention is that, depending on the selection, within the radio frequency detector. Drug delivery The microcatheter is described in co-pending US patent application Ser. No. 08 / 857,043, filed May 15, 1997, under the name of John Kucharczzyk and Michael Mosley, with case number SL WK 600.392US1. It is possible to attach a receiver coil that can be used in the process for sensing the actual drug administration and movement according to the invention.
[0020]
FIG. 1 is desirable according to the present invention. Drug delivery 1 shows a catheter 2 for medical use. The catheter 2 includes a central lumen 4 that extends out from the port 6 at the tapered end 8 of the catheter 2. The first microcoil 10 is wound around the lumen 4 so that the individual coils 12 are inclined in the direction opposite to the tapered end 8 as a whole. A lead wire 14 is connected to the first microcoil 12. The second microcoil 16 is wound around the lumen 4 and the individual coils 18 are inclined in the direction of the tapered end 8 as a whole. The pair of first microcoil 10 (and 32, collectively referred to as 10) and second microcoil 16 (and 18, collectively referred to as 16) form an opposing pair of microcoils. To do. The individual coils 10 and 32 of the relatively proximal set of microcoils 10 and the individual coils 16 and 18 of the second microcoil 16 are orthogonal to the lumen 4 that effectively forms the axis of the catheter 2. It has an angle (positive and negative) relative to AB. Note that paired coils can have different spacing between adjacent coils (eg, spacing between 13 and 15 compared to spacing between 15 and 17). This difference in spacing will be discussed later. The lead wire 20 is passed from the second microcoil 16 to the electronic circuit 22 in the same manner as the lead wire 14 from the first microcoil 10. The first microcoil 10 and the second microcoil 16 are clearly separated by a space in which the RF response field from the coils 10 and 16 (not shown in the figure) is the most. large. From microcatheters 24, 26, 28 and 30 Drug delivery Is most effectively observed in the space B outside the catheter 2 in the zone formed by the opposite ends 32 and 34 of the two microcoils 10 and 16 (respectively).
[0021]
The microcoils 10 and 16 are embedded in a support material 34 such as a polymer material, a composite material, or an inorganic material (for example, an inorganic oxide). The composition of this material must be biocompatible, and polymeric materials such as polyamides, polyesters, poly (methyl) acrylates, polyvinyl acetate, cellulose acetate, or other organic polymers that are biocompatible are desirable. This support material 34 can also constitute the composition of the tapered end 8. Leads 36 and 38 connect circuit 22 to an external controller and / or power source. The ends 24a, 26a, 28a and 30a of the microcatheters 24, 26, 28 and 30 are Drug delivery The connection to the system or drug or drug delivery pump is shown omitted.
[0022]
The inter-microcoil spacing B (relative to the intra-microcoil spacing) between the opposing microcoils is typically Drug delivery MR by type or regardless of catheter or other device Applicable Depending on the type of treatment performed by the correct device 2. The parameters considered for optimization, particularly with respect to the position of the microcoil, include at least the desired diameter of the magnetic field from the coil, the strength of the magnetic field, the width of the magnetic field, the number of magnetic fields (eg, of the pair of opposing microcoils Number), the position of a pair of microcoils relative to the distal end of the catheter, the position of the microcoil relative to the drug or point of administration of the drug, and the like. These considerations include engineering such as coil thickness and size, coil composition, circuit placement (whether in the catheter or connected to external circuitry via leads), and composition of other materials in the catheter structure. Participatory and other design considerations.
[0023]
A preamplifier coupled to the plastic layer 35 (shown here as a continuation of layer 8), leads 36 and 38 microcoil at the most proximal end (part from the tip) within the catheter structure. , And / or a second insulating layer 37 (eg, of layer 34) that electrically insulates lead 36 and 38 and / or shield 39 that forms a layer around the preamplifier (at a distance radially away). Plastic, ceramic or biocompatible material) as well as the description of the support material.
[0024]
Inter-coil spacing and inter-coil spacing (which overlaps coil-to-coil and micro-coil considerations such as with respect to coil diameter) must also be considered to optimize the design of the system of the present invention.
Coils, particularly coils such as intravascular RF coils in MRI, can be very useful for MR imaging of luminal morphology with a limited field of view (FOV) and high signal-to-noise ratio and spatial resolution. The most promising basic coil design for this type of purpose is the previously published (Martin, supra) opposing solenoid coil. The reported coil is two equally wound solenoids of the same shape and uniform coil diameter placed along a common axis with opposite polarity. This special coil design has plenty of room for improvement based on considerations not disclosed in the reference material. One criterion for improvement for the functional characteristics of the signal is that a better intravascular coil can be obtained by optimizing the current distribution in the coil. Analytical formulas for the magnetic field outside the cylindrical coil have already been developed to optimize the current distribution on the surface of the cylinder (eg assuming the underlying device such as a catheter is cylindrical) for the required magnetic field constraints. It is desirable to use this for this new coil design. The coil thus optimized improves the magnetic field strength and the magnetic field uniformity. Certain uses of the apparatus of the present invention are represented by the generation of an image or certain information (eg, signal density differences) in the image. Drug delivery Uniform magnetic field strength is particularly important because it uses density readings and derivatives to provide speed or degree of therapeutic effect.
[0025]
The shape of the RF coil is based on a cylinder with a small limited length in this analysis. Current density is limited to the cylindrical surface of the coil. Solving the problem of the corresponding static magnetic field in the cylindrical coil of radius a, the radius component (> a) of the magnetic field outside the RF coil is given by the following equation.
[0026]
[Expression 1]

[0027]
Here, JΦ (m, k) represents an azimuth angle component of the surface current density defined by the following formula in the above formula.
[0028]
[Expression 2]

[0029]
Im (t) and Km (t) represent two types of m-order modified Bessel functions, where m is an integer (eg, 1, 2, 3,...), And I ′m ( t) and K′m (t) represent the first derivatives of Im (t) and Km (t).
The stored magnetic energy associated with the coil is shown in the form of a series expansion equation as follows:
[0030]
[Equation 3]

[0031]
Especially for solenoid coils or z coils whose surface current density has no z component, the above equations for energy and magnetic field are simplified as follows:
[0032]
[Expression 4]

[0033]
In order to find an optimal (or minimal energy) solution for the current density distribution of a cylindrical surface that satisfies a set of magnetic field constraints at several spatial locations, an energy functional configuration is defined as follows:
[0034]
[Equation 5]

[0035]
Here, a set of L multipliers is represented. The magnetic field constraint conditions define a set of desirable magnetic field values at several points in the target imaging volume.
In order to minimize the energy functional with respect to the current density functional, the following variation is added to the current density functional.
[0036]
[Formula 6]

[0037]
The optimized current density is then expressed as follows for the L multiplier:
[0038]
[Expression 7]

[0039]
Since JΦ (z) is asymmetric with z for the desired magnetic field distribution, its Fourier component can be expressed as follows:
[0040]
[Equation 8]

[0041]
Inserting the formula for the current density into the magnetic field constraint formula gives a set of linear equations for the multiplier λ.
[0042]
[Equation 9]

[0043]
When the linear equation for the magnetic field constraint condition is solved for the Lagrange multiplier, the current density can be determined from an equation including the Lagrange multiplier. In the case of an RF coil with a limited length (L), the surface current density can be expanded to a desired order with a sine series formula.
[0044]
[Expression 10]

[0045]
Here, the value of kn is as follows.
[0046]
[Expression 11]

[0047]
Jn represents an expansion coefficient relating to current density.
Next, the general formula in the k-space can be expressed as follows for the surface current density of the limited-length coil.
[0048]
[Expression 12]

[0049]
Here, Ψn (k) is an odd function of k defined by the following equation.
[0050]
[Formula 13]

[0051]
Using the new function expansion equation, the equations for stored magnetic energy and magnetic field can be expressed as:
[0052]
[Expression 14]

[0053]
The desired receive field distribution outside the coil can be converted to several field constraint points at several selected locations. For each design, the magnetic field constraint condition points are defined as follows:
[0054]
[Expression 15]

[0055]
The constraint conditions define the homogeneity of the coil magnetic field required in the gap in addition to the relative magnetic field strength. The magnetic field constraint conditional expressions regarding the radius component at various points can be expressed as follows.
[0056]
[Expression 16]

[0057]
For convenience, both the magnetic field equation and the energy equation are represented in a matrix. Between the two equations, the matrix elements of b are shown as follows:
[0058]
[Expression 17]

[0059]
The stored magnetic energy of the coil is as follows.
[0060]
[Formula 18]

[0061]
Here, the energy matrix element is expressed by the following equation.
[0062]
[Equation 19]

[0063]
The energy functional including the magnetic field constraint conditional expression is defined as follows.
[0064]
[Expression 20]

[0065]
In order to obtain the minimum condition of the energy functional, the F functional is minimized with respect to the current string vector J. That is,
[0066]
[Expression 21]

[0067]
Thus, the following minimum condition equation including the current density is reached.
[0068]
[Expression 22]

[0069]
The following magnetic field constraint condition formula is used as another independent equation.
[0070]
[Expression 23]

[0071]
First, the Lagrangian multiplier can be solved by the following linear equation combining the above minimum conditional expression and magnetic field constraint conditional expression.
[0072]
[Expression 24]

[0073]
Using this value for the Lagrange multiplier, the surface current density of the coil can be determined as follows.
[0074]
[Expression 25]

[0075]
The current density is as follows.
[0076]
[Equation 26]

[0077]
The total current for half of the coil is given by:
[0078]
[Expression 27]

[0079]
If the number of turns is set to Nturn, the individual currents can be determined as follows:
[0080]
[Expression 28]

[0081]
The inductance of the N-turn coil, which is half of the coil, is as follows.
[0082]
[Expression 29]

[0083]
In order to determine the position of each current abdomen, the following current density integral is calculated from the center of the coil.
[0084]
[30]

[0085]
This integration makes it possible to determine all the spatial spacings across N different discrete current wire loops. The exact position of each wire along the z-axis can be determined as the center of mass for that interval.
[0086]
[31]

[0087]
In short, the means for optimizing the in-coil distribution of coils within each microcoil of a pair of opposed microcoils is as above with respect to the effect of current, coil characteristics and positioning and design of individual coils or windings. It can be based on any or an alternative mathematical model. This special composition was developed for a cylindrical RF coil, and this technique optimizes the design of the current abdominal position of intravascular, intracavitary, intraparenchymal or intravascular MR imaging coils. It will be a simple procedure.
[0088]
Referring to FIGS. 4 (a, b and c), it will help to understand how the modification in the coil design improves the performance of the catheter of the present invention. FIG. 4a shows the magnetic field strength (y-axis) as a function of distance from the midpoint of the gap (eg, the middle between the closest ends of opposing microcoils separated by a distance of 2d represented by space 19 in FIG. 1). Is shown. FIG. 4a shows the magnetic field strength relationship in a cylindrical device with opposing pairs of microcoils with the same individual winding size and spacing between the windings. As can be seen from FIG. 4a, the maximum magnetic field strength Fmax has a relatively steep peak, and the magnetic field strength decreases as the distance from the center of the gap (x = 0) changes. In the middle between the middle of the gap (distance from the nearest end of the opposing microcoil) and the end of the opposing microcoil, the magnetic field strength is typically reduced from 25% to 50% of Fmax. . This rapid and large field strength change can diminish the ability of the device to provide image type and quality in certain procedures. FIG. 4b shows the ideal shape of the magnetic field strength distribution obtained by designing the position, shape, thickness and distribution of the microcoil according to the modeling considerations discussed above. Since the effects of individual windings can be calculated mathematically as shown above, the individual effects can be added to determine the effective magnetic field strength. The mathematical addition of the effects of the individual windings can be adjusted to a more realistic magnetic field effect obtained from coil combinations, taking into account some interactive effects. Further reachable magnetic field strength distribution is shown in FIG. 4c. This figure shows a significantly improved magnetic field strength distribution, although less ideal. FIG. 4c shows the relationship between the magnetic field strength and the position along the cylindrical device, the device having a pair of microcoils with a spacing of 2d between the proximal ends of the opposing coils, The microcoil has coil winding portions (for example, in FIG. 1, for example, 13 in the interval between the windings 13 and 15 different from the interval between the same microcoil windings 15 and 17). , 15 and 17). The magnetic field strength is more uniform near the gap center (x = 0) than in the case of the opposing microcoil structure shown in FIG. 4a. The field strength decreases as the distance from the gap center increases, but the rate of decrease is greater than the ideal result of FIG. 4b, but less than the uniform coil winding of FIG. 4a. The decrease in magnetic field strength between the gap center and the d / 2 position, which is half the distance from the gap center to the near end of the microcoil, is expected to be 20% or less. The reduction between Fmax and the magnetic field strength at the d / 2 point in the middle between the midpoint of the gap and the near end of the microcoil is preferably less than 17%, more preferably less than 15% and even less than 12% The most desirable is 10% or less than 8%.
[0089]
The device according to the invention consists of elements having at least one pair of opposed RF receiver microcoils spaced between each microcoil of a pair of microcoils, each said RF receiver microcoil being at least three individual For use in living bodies having a coil, wherein the at least three individual coils are spaced between adjacent coils such that the distance between at least two pairs of individual coils in the microcoil is at least 10% different. It can also be described as a medical device. To improve the results of the magnetic field strength distribution in the gap, the spacing between the pair of individual coils (or windings) is a line that lies in a plane parallel to the axis of the cylinder (or other shape) to which the microcoil belongs. , And can be at least 12%, 15%, 20% or more different from other spacings between adjacent windings.
[0090]
Another design configuration that can be used for a useful structure in the practice of the present invention is a configuration with two layers of microcoils in the region forming half of a pair of microcoils. That is, the first set of microcoils inclined in the gap direction is arranged in one layer of the MR observable device, and the second set of microcoils (for example, one set of windings) is also inclined in the gap direction. Can be placed in an insulating layer overlying or underlying the first set of microcoils. The spacing between the coils in a set of similarly inclined microcoils may be the same or different widths, and may be the same or different spacings, either the same angle or different angles (both tilted in the gap direction or both Both have to lean in the opposite direction of the gap). The device can have at least one set of microcoils, and at least four of which at least three pairs of microcoils have at least three spaces, space 1, space 2, and space 3, between adjacent windings. And at least one of the at least three spaces has a different dimension than at least one other of the spaces.
[0091]
Although some of the technical and structural considerations known in the art are used in the new structural design of the present invention, many technical and structural considerations known in the art are included in the practice of the present invention. Can do. For example, the composition of lumen 4, support material 34 and catheter casing 40 can be selected from known biocompatible materials developed for medical use. The microcoils and circuits that form part of the catheter system can also be provided using techniques that have not been previously used in the field of medical devices. For example, the microcoil can be provided by wrapping filaments of electrical conductors (especially copper, copper cladding and other RF antenna materials known in the art) or by forming filaments over the lumen. right. Such formation processes include deposition processes, growth deposition processes, deposition etch processes, microlithography, masking deposition, and the like. Deposition processes include plating, electroless plating, sputtering, nucleated growth (eg, 4,775,556 and 4,710,403), high energy deposition or etching processes (eg, US Pat. No. 5,389). 195 and 5,332,625), chemical deposition and etching processes, and the like. The techniques for making circuits and wiring shown in US Pat. Nos. 5,106,455, 5,167,625 and 5,269,882 are generally used to deposit circuits on filament products and surfaces. Examples of other useful technologies.
[0092]
FIG. 2 is a cross-sectional view of an intermediate portion of a catheter 100 according to one configuration that can be used in the present invention. The microcatheter 102 is shown warping against an internal guide element or deflector 106 such that one end 105 of the microcatheter 102 extends out of the catheter 100 from a hole 108 in the wall of the catheter 100. The microcatheter 102 is supported by the deflector 104 from the contact 103 while being warped by the deflector 104. The hole 108 passes through what is shown in FIG. 2 as the three layers 110, 112 and 114 of material that make up the substantial wall of the catheter 100. The deflector 104 serves as a guide for guiding the microcatheter into and through the hole 108. There is one hole and deflector for each microcatheter that goes out of the catheter (these microcatheters can have their own microcoil), and these microcatheters (not shown in the figure) are catheters Extends from 100 to the outside. However, this does not apply to cases where two or more microcatheter exits from a single hole. Drug delivery ) Is not desirable because it will occur in a small area relative to the surface of the catheter 100. The device can have at least three deflectors to define the direction of each of the at least three microcatheters from at least three separate ports.
[0093]
Also shown in FIG. 2 is a pair of microcoils 116 and 118. These microcoils 116 and 118 are shown embedded in the layer 112 of the catheter 100. In order for the imaging and positioning function of the catheter 100 to work optimally, it is highly desirable that the signals emitted by the microcoils 116 and 118 be as accurate and clear as possible. The presence of other circuits and wires in the catheter can interfere with this type of performance and must be specifically considered to prevent problems with electrical and electronic functioning of various parts of the catheter and its subcomponents. I must. For example, the wires 120 and 122 connected to the ends 124 and 126 of the microcoils 116 and 118, respectively, are in contact with the microcoils 116 and 118 except at points for electrical connection (eg, ends 124 and 126) Must not. This can be made possible in various ways based on the implementation of the present invention. The potential for this type of problem to occur is structurally small in the proximal microcoil 116. This is because the end 124 can be connected to the wire 122 without passing through the coil circuit. Therefore, wire 122 is on the same layer as coil 116. 112 Can be arranged. In the case of the distal microcoil 118, the wire 120 must be passed over the two coils 116 and 118, and may contact the microcoils 116 and 118 or easily interfere with the signal from the microcoil. . To prevent this, the microcoils 116 and 118 are shown in a single layer 112, but the wire 120 from the distal microcoil 118 is connected to the coils 116 and 118 or other circuitry within the catheter 100. Layers to reduce or eliminate electrical or electronic interference with or interaction with (not shown in the figure) 114 Shown in If the need for proper positioning of the elements is recognized, each element can be separated into separate layers using a number of techniques available in common manufacturing techniques. For example, after installing the microcoil (eg, by wrapping, depositing, or etching), the microcoil can be confined in one layer (eg, layer 112) with a polymer or other insulating material. Once this protective layer or enclosure is established (maintaining appropriate electrical connection points for other electrical or electronic connections), other wiring or circuitry may be placed over this encapsulating enclosure (eg, layer 112). Can be built. This additional wiring or circuit is a process similar to that used to make the coil, or wrapping, application of a pre-made circuit, deposition of the circuit or wire element, etching of the circuit or wire element and others known in the art Or other processes known in the art such as microstructural techniques. The main purpose of using this selective structure in the implementation of some configurations of the present invention is to place circuits and / or wires in different layers of the catheter (even with the same polymer binder composition). is there. Wiring or additional circuit placement is intended to minimize crosstalk, interference, interaction or other related effects that impair microcoil and circuit performance. In consideration of the above, an inherent interference wave effect or magnetic field effect can be taken into consideration in the layout design of each element.
[0094]
MR image surveillance according to some aspects of the invention Drug delivery A composite catheter involves a composite device (needle or catheter) or other device incorporating a micro-imaging coil for MR imaging (spectroscopy) monitoring or other physiological monitoring during treatment. The micro coil can be interfaced to a conventional MR scanner to image pathological changes in the immediate vicinity of the coil as well as the treatment site with a very high signal-to-noise ratio without interfering with the dosing process . This type of device will be in great demand in the near future for many neuroparenchymal or intravascular treatments.
[0095]
One of the composite devices is shown schematically in FIG. As shown in FIG. 1, the catheter is a physiological measurement, Drug delivery There are a number of micro-sized tubes 24, 26, 28 and 30 in the lumen 4 to perform various functions such as material pulling, sampling, temperature relaxation or fluctuation, electrical stimulation, and the like. At the tip of the catheter is a microcoil 10 with a small preamplifier 22 for MR imaging and spectroscopy.
[0096]
Generally speaking, this type of composite device (ie, catheter) includes at least one micro-imaging coil that can be broken down into the following four modular parts as shown in FIG.
1) Optimized imaging coil or electrode
2) Preamplification and decoupling integrated circuit
3) Signal transmission and shielding
4) Remote matching circuit
The above four parts are not necessarily separated from each other in the case of individual composite device designs, but separate the modules only to facilitate the following description.
[0097]
In most cases, some of these modules are often integrated into one composite device. The microcoil for MR imaging can be a single loop, stranded wire, or one of two opposing solenoids. All of these coil designs are very sensitive to the proximity region of the coil. The details of the spatial sensitivity trends of an individual coil depend on its conductor pattern.
[0098]
In the case of opposing solenoids, the primary magnetic flux for reception is ejected in the gap between the two coils (typically in the direction perpendicular to the winding or to the axis of the cylindrical device on which the coil is wound or formed). ). The number of windings required is at least 3 per coil, preferably between 3 and 20, more preferably between 4 and 16, most preferably between 5 and 12 and the diameter of each coil is possible If it is 0.1 to 2.4 mm, a diameter of 0.3 to 2.0 mm is more preferable, and a diameter of 0.5 to 2.0 mm is most preferable. By depositing the coil on the surface, depending on the size of the catheter, a thin layer of material can be deposited as a coil (for example, from a few microns thick to the same thickness as the coil width) to occupy the volume occupied by the coil. The coil can be made smaller and the width of the coil widened. The coil is wound or deposited on a small diameter cylindrical surface, but there are several degrees of freedom for optimization. For solenoid coil designs, one degree of freedom is the spacing between the windings. To some extent, the design of the micro-sized coil can be numerically optimized to produce spatially desirable receive field patterns (uniformity) under the geometric constraints imposed by a particular clinical device. it can. Using the target field method, the conductor pattern can be numerically optimized to approximately match the target received field pattern. Coils within a microcoil have a spacing between adjacent coil centers of 2.0 times the coil diameter (so that the spacing between the outer surfaces of adjacent coils is equal to the diameter of the individual coils) to 10 times (adjacent). Can be formed or wound so that the spacing between the outer surfaces of the coils is 9 times the diameter of the individual coils. The spacing is preferably between 2.5 and 8 times the diameter, more preferably between 3 and 6 times the diameter. As previously mentioned, the prior art suggests that the use of microcoils with a diameter of less than 2.8 mm is undesirable. If the coils are opposed and inclined, the coil diameter is preferably 2.4 mm or less in the practice of the present invention. It is also novel in the present invention to provide microcoils with different intercoil spacing in each half of the pair of coils and to have a desired coil diameter greater than 2.4 mm. For example, the coil can be simply 4.0 mm, 3.5 mm or 3.0 mm, including smaller desirable dimensions, if the inter-coil spacing varies according to the lessons of the present invention.
[0099]
Furthermore, the coil wire material can be a non-magnetic metal or a metal alloy with a magnetic susceptibility similar to human tissue. For example, desirable materials include copper, silver, aluminum, and copper-aluminum composites. Both copper and silver are diamagnetic, and aluminum is paramagnetic. To minimize magnetic field disturbances, the coil conductors can be made to have multiple concentric layers of different metallic materials (Cuχ = −9.7 × 10 ^-6 And Alχ = + 20.7 × 10 ^-6 ). The exact layer thickness or radius of the different metal components can be numerically optimized depending on the size of the wire. For a zero susceptibility cylindrical wire, the radius ratio is given by:
[0100]
[Expression 32]

[0101]
In order to minimize the mutual coupling between the microcoil and the volume coil used for image excitation, it is desirable to incorporate a decoupling circuit into the microcoil. During excitation, the decoupling circuit element makes the microcoil invisible to the volume coil by removing the resonance frequency of the imaging coil from the transmit RF frequency. One design that meets the coil decoupling requirements is shown in FIG. If the device includes a PIN diode, denoted D, in series with two capacitors (C1 and C2), the imaging coil is shown abstractly as L. The PIN diode D is actively switched on and off by an external control voltage Vd across the diode. When the diode D is switched on, the coil L and the two capacitors C1, C2 constitute a resonant circuit tuned to the frequency. This is an improved version of a circuit that includes a preamplifier. The device can also include a PIN diode in series with only one capacitor. The diode is actively switched on and off by an external control voltage. An FET (field effect transistor) may be provided for RF frequency signal amplification. To protect the FET element or other type of preamplifier module during RF excitation, a cross diode can be placed in front of the FET to bypass the excessively induced current during RF transmission.
[0102]
The entire coil can be combined. In other words, the entire imaging coil can be made up of multiple coil elements connected in series or in a phased array for simultaneous imaging at multiple locations along the catheter. All of the plurality of coils may be geometrically the same or different. The imaging coil can also be non-local. That is, the coils can be spatially distributed along a significant length of the catheter (especially by considering the modeling shown above). For this reason, there are many options for the active coil element, such as a stranded wire, two parallel wires, a coaxial cable, and combinations thereof.
[0103]
In addition to the variety of imaging coil element options, a variety of other elements such as microelectrodes can be incorporated into a device for cell or membrane potential measurement, pressure / flow monitoring or other physiological monitoring.
In order to optimize the signal to noise ratio (S / N) or to minimize the noise value, the detected MR signal is immediately amplified as close as possible to the coil elements (eg preamplification). Is desirable. The actual catheter shape is not sufficient to use a conventional amplifying element. In order to minimize the size of the electronic elements used for preconditioning of various signals such as preamplification, an integrated circuit module is incorporated near the imaging module. The integrated circuit module includes preamplifiers (or RF frequency devices) and other auxiliary devices assembled on a silicon chip. The silicon chip is preferably less than 4 mm2. The integrated circuit module is preferably housed in a small non-magnetic casing that is both geometrically compatible with the particular equipment design. One of the simplest devices is one that contains only a single FET element. In order to assemble more complex circuits and improve performance, with the help of integrated circuit technology, the most elements can be incorporated into a single silicon module.
[0104]
The preferred transmission module is part of a flexible cable along the catheter for transmitting the RF signal detected for MR imaging from the coil to the remote terminal for subsequent signal amplification and other processing. . In the preferred design, all elements of the cable are incorporated into the catheter. One desirable requirement of the cable is to reduce signal attenuation for fine MR signals while at the same time reducing noise contamination. Another requirement for the cable is to minimize interference with the flexibility and stiffness of the catheter. To meet this requirement, the device has many different alternatives as follows.
[0105]
1) A three-layer coaxial cable (a cable in which a central conducting wire is surrounded by a concentric two-layer shielding material). A variation of this cable is one in which the central conductor is spirally wound along the central axis of the cable.
2) Shielded twisted cable (cable in which the two central strands are surrounded by a concentric layer of shielding material). One variation of this cable is that two wires are spirally or spirally wound along the central axis of the cable).
[0106]
3) Shielded parallel bipolar cable (cable in which two parallel bipolar wires are arranged symmetrically with respect to the central axis and surrounded by a layer of concentric shielding material). One variation of this cable is that two wires are spirally or spirally wound in parallel along the central axis of the cable).
The shielding layer can be a thin braided wire layer, a metal film layer, or other shielding material known in the art that can be supplied in dimensions compatible with the practice of the present invention (which can be grounded if desired). .
[0107]
Yet another useful design is the idea of placing all elements at a remote device (or distal end). The schematic diagram shown schematically in FIG. 3 includes imaging coils (micro and macro), transmission lines, phase shift networks, tuning and decoupling circuits and baluns (balanced unbalanced impedance matching transformers). Z represents the tuning element (L or C) as part of the decoupling circuit. The combination of the transmission line and the phase shift network exhibits ¼ or half wavelength characteristics.
[0108]
A remote alignment device is a device located at the remote end of the device. This remote device can be used as a special tuning device for the tip imaging coil or as a detuning (or decoupling) device. The remote matching device allows for effective impedance transformation of the transmitter for coil impedance matching and frequency tuning. In this design, both transmission lines and remote devices are used for tuning and detuning. In order to take advantage of the characteristics of the transmission line, a 1/4 or half wavelength wire of the radio frequency is used. Otherwise, a transmission line with a phase shift network that exhibits the same effective quarter or half wavelength behavior can be used. Coil tuning can be done using capacitors or inductors. Furthermore, the size of the device is not geometrically limited. The device size of this module is not a problem, so more conventional electronic devices can be used. Depending on the specific design, the remote device can be very important or not important.
[0109]
Finally, a stabilization mechanism is incorporated into the catheter tip. Desirable stabilization devices can be mechanically driven or made of shape memory alloy and controlled by an external voltage signal.
[Brief description of the drawings]
FIG. 1 is based on the implementation of the present invention Drug delivery 1 shows a catheter.
FIG. 2 is a cross-sectional view of the catheter highlighting the microcatheter outlet of the catheter and the wiring of the catheter.
FIG. 3a is a schematic circuit diagram of a catheter of the present invention.
FIG. 3b is a schematic circuit diagram of the catheter of the present invention.
FIG. 4a shows a graph of magnetic field strength versus distance from the gap center between two opposing pairs of microcoils for three microcoil structures.
FIG. 4b shows a graph of magnetic field strength versus distance from the gap center between two opposing pairs of microcoils for three microcoil structures.
FIG. 4c shows a graph of magnetic field strength versus distance from the gap center between two opposing pairs of microcoils for three microcoil structures.

Claims (16)

A compatible with the magnetic resonance imaging treatment apparatus for use in vivo, the device comprises an element having an RF receiver microcoils to the relative direction of at least one pair, RF receiver opposing said pair The microcoil has a plurality of coils along a common axis, and these coils have a reverse polarity between the pair of microcoils, and the microcoil is between each microcoil of the pair of microcoils. in a space, winding of the microcoil, it has a diameter of less than 2.4 mm, furthermore,
Within the device, at least three ports are provided for drug delivery by at least three microcatheters through these ports, and through the at least three ports within the device. A device for use in vivo compatible with magnetic resonance imaging procedures, wherein at least three deflectors are provided for directing each of the at least three microcatheters.   The apparatus comprises a catheter having at least one lumen, and the at least one pair of microcoils are radially disposed about the at least one lumen, the coils being greater than 0.1 mm and greater than 2.4 mm The device of claim 1 having a small diameter. At least one drug delivery port, Ru least some drugs are arranged to be delivered to the outside from the device in the space between the microcoil Tei delivered from the port, of claim 1 apparatus. There are a plurality of catheters in the device, the catheters being at the ends of at least one pair of microcoils that form a space between each microcoil in the at least one pair of microcoils, by a surface extending radially from the catheter. The device of claim 2 , wherein the device extends out of the device to deliver at least some liquid material within the volume to be formed. The apparatus of claim 4 , wherein the apparatus generates a uniform receive field within the volume in response to radio frequency transmission. The apparatus of claim 1 , wherein the apparatus comprises a catheter having a lumen, and wherein the at least one pair of microcoils are embedded in a bonding material surrounding the lumen. 6. A device according to any one of the preceding claims, wherein the at least one pair of microcoils is electrically connected to a preamplifier within the portion of the device that is inserted into the living body. 6. A device according to any preceding claim, wherein an electrical connection is in the device and at least a portion of the electrical connection is embedded in the device. At least one set of microcoils comprising half of the at least one pair of microcoils comprises at least four windings with at least three spaces of dimensions 1, 2, and 3 between adjacent windings. 6. The apparatus according to any one of claims 1 to 5 , wherein at least one of the at least three spaces is not equal to a dimension of at least one other of the spaces.   Comprising at least one pair of opposing RF receiver microcoils with a space between each microcoil of the paired microcoils, each of said RF receiver microcoils comprising at least three individual windings; In vivo use wherein the at least three windings of the microcoil are spaced between adjacent windings such that the spacing between at least two pairs of individual windings within the microcoil is at least 10% different Device to do. The at least one RF receiver microcoil has a space between the paired microcoils, and the at least one RF receiver microcoil exhibits a maximum magnetic field strength within a cylindrical volume surrounding the space. Between the midpoint of the space and the proximal end of the microcoil that forms part of the at least one pair of RF receiver microcoils along a line parallel to the longitudinal axis of the device that produces a magnetic field strength A second magnetic field strength is generated at an intermediate position, and the second magnetic field strength along a line parallel to the longitudinal axis of the device is less than 40% below the maximum value of the magnetic field strength between the microcoils. 10. The apparatus according to 10 . The apparatus of claim 11 , wherein the second magnetic field strength is not greater than 20% below the maximum magnetic field strength. 13. Apparatus according to any one of claims 10 to 12, wherein the microcoil winding diameter is less than 2.4 mm. There is at least one drug delivery port in the device, and the at least one drug delivery port has at least some drug administered via the port between the microcoils of the at least one pair of microcoils. 14. The device of claim 13 , arranged to be dispensed from the device in a volume above a space. At least one set of microcoils comprising half of the at least one pair of microcoils comprises at least four windings with at least three spaces of dimensions 1, 2, and 3 between adjacent windings. , wherein at least one of the at least three spaces, not equal to the dimensions of the other of the at least one space of said space, according to claim 1. A device adapted for magnetic resonance imaging and used in vivo, the device comprising an element having at least one pair of opposing RF receiver microcoils, wherein each microcoil is on a common axis A plurality of coils along the opposite polarity between the pair of microcoils, with a space between each microcoil of the pair of microcoils, connected to the microcoil in the device There is a layer radially outside the wire and / or preamplifier, the layer being an RF shield for the wire and / or preamplifier coupled to the microcoil, and the layer coupled to the microcoil A device used in vivo adapted for magnetic resonance imaging procedures , electrically insulated from said electrical wires and / or preamplifiers .

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